1. Field of the Invention
This invention relates to security substrates, particularly thermally imageable substrates useful for secure point of sale imaging in diverse applications such as mailers and lottery tickets.
2. Description of the Background Art
A variety of constructions of secure substrates such as lottery tickets are known. U.S. Pat. No. 6,308,991, for example, describes a lottery ticket with an authentication feature of a bar code covered by a scratch off layer. The ticket indicia is pre-printed and covered by a scratch-off layer to obscure the pre-printed indicia.
Alternative lottery ticket designs include pull tabs that cover pre-printed indicia. Examples of such constructs are taught in U.S. Pat. Nos. 6,390,916 and 6,379,742.
A need exists to be able to securely print information indicia to a secure substrate at the point of sale to minimize the need or extent of pre-printing required and to add versatility to gaming systems.
U.S. Pat. No. 4,677,553 teaches a scratch off opaque overlay responsive to thermal printing to print confidential information into a concealed area. Scratch off ink of Electron in Carlstradt, N.J. taught as the scratch off material.
The above systems have the drawback that the removed ink create debris, are not convenient for the consumer, and the removal process can damage the image if excessive force is used with a sharp instrument to scratch off the removal ink.